A few times I’ve switched from the default private networking (NAT with port forwarding) to public networking (bridged) in the Vagrantfile. When switching *back* to private networking, I wasn’t able to SSH back into the machine (i.e, “vagrant up” will time out).

Assuming you’re using a Linux Mint guest (or other Debian-based) OS, a fix for this is to open the /etc/network/interfaces file and remove anything in between the #VAGRANT BEGIN and #VAGRANT END section. Next, run vagrant reload from the host OS to reload the guest with the updated network interface configuration.